python3 preprocess.py -train_src data/cnndm/train.txt.src \
                     -train_tgt data/cnndm/train.txt.tgt.tagged \
                     -valid_src data/cnndm/val.txt.src \
                     -valid_tgt data/cnndm/val.txt.tgt.tagged \
                     -save_data data/cnndm/CNNDM \
                     -src_seq_length 10000 \
                     -tgt_seq_length 10000 \
                     -src_seq_length_trunc 400 \
                     -tgt_seq_length_trunc 100 \
                     -dynamic_dict \
                     -share_vocab \
                     -shard_size 100000
